1. Technical Field
The present invention relates to a liquid ejecting apparatus such as an ink jet type printer and a control method thereof and in particular, to a liquid ejecting apparatus in which a maintenance process which restores ejection capability of a liquid ejecting head is performed, and a control method thereof.
2. Related Art
For example, a liquid ejecting apparatus is an apparatus which is provided with a liquid ejecting head capable of ejecting liquid from a nozzle and ejects a variety of liquids from the liquid ejecting head. As a representative example of the liquid ejecting apparatus, an image recording apparatus such as an ink jet type printer (hereinafter simply referred to as a printer) which is provided with an ink jet type recording head (hereinafter simply referred to as a recording head) as the liquid ejecting head and which performs the recording of an image or the like by ejecting and impacting ink in the form of liquid from the nozzle of the recording head onto a recording medium (an impacting target) such as a recording paper, can be given. Also, in recent years, the liquid ejecting apparatus has been applied not only to the image recording apparatus, but also to a variety of manufacturing apparatuses such as an apparatus for manufacturing a color filter of a liquid crystal display or the like.
Here, the above-mentioned printer is provided with the recording head which has a series of ink flow paths extending from a reservoir to the nozzle through a pressure chamber, a pressure generation section (for example, a piezoelectric element) for changing the volume of the pressure chamber, and the like, a driving signal generation section which generates a driving signal for driving the pressure generation section, and the like. Then, the printer is constituted so as to give rise to a pressure variation in the ink in the pressure chamber by applying a driving pulse which is included in the driving signal to the piezoelectric element and eject ink from the nozzle with use of the pressure variation. In such a printer, there is a case where the surface (meniscus) of ink exposed at the nozzle is exposed to the atmosphere, so that a solvent evaporates, thereby thickening the ink, or air bubbles are mixed into the pressure chamber or the like, so that a change in pressure is absorbed by the air bubbles, whereby poor ejection occurs such as non-ejection of ink (so-called dot omission) or curving of a flying direction of the ejected ink.
For this reason, in order to maintain excellent ejection of ink by preventing the above-mentioned poor ejection, techniques related to various maintenance processes have been proposed. For example, a cleaning process is performed which temporarily seals the nozzle by a cap, depressurizes the inside of the cap in the sealed state, and forcibly discharges thickened ink or air bubbles by performing idle ejection of ink by applying an ejection driving pulse to the piezoelectric element and thereby giving rise to a pressure variation in the ink in the pressure chamber. However, even if the above-mentioned cleaning process is executed, it is difficult to completely remove the air bubbles. In addition, the idle ejection is to eject ink for the purpose of restoring ejection characteristics of the recording head to a normal state, separately from ink ejection for the printing of an image or the like on the recording medium, which is the original purpose of the printer.
Therefore, in this type of printer, separately from the above-mentioned cleaning process, a maintenance process is performed which is called a flushing process which forcibly ejects ink from the nozzle. Specifically, after execution of the above-mentioned cleaning process or execution of initial filling at the time of exchange of an ink cartridge is performed, or for every predetermined printing unit during a printing operation (during a recording operation), for example, every time printing is performed for a constant period of time, every time the predetermined number of times of passes (scanning of the recording head) is performed, or every time the predetermined number of pages is printed, the recording head is moved up to an ink receiving member which is located at a position deviated from the recording medium and ink is repeatedly idle-ejected at the position. With respect to the flushing process, there is an air bubble removal flushing process mainly aimed to remove air bubbles in ink, or the like, other than a flushing process for thickened ink discharge, which idle-ejects ink for the main purpose of discharging ink thickened in the vicinity of the nozzle (for example, JP-A-2009-73074).
However, in the above-mentioned air bubble removal flushing process, if a change in pressure is increased so as to further increase an air bubble removal effect, residual vibration is also increased by a corresponding amount. If a process is moved to the print processing in a state where the residual vibration is not controlled, there is a concern that the weight or the flying speed of ink which is ejected will become unstable. For this reason, there is a problem that a time for attenuating the residual vibration needs to be set after the air bubble removal flushing process, so that it is not possible to transition quickly to the print processing.
Also, in an evaluation of the reliability of the above printer, an index which is called a MPBF (Mean Pages Between Failures) is sometimes used. The MPBF represents an average value of the number of pages of the recording papers which can be printed between adjacent breakdowns which are generated under use conditions prescribed in design within a period of the life-span of the printer as an apparatus (or between the first operation start after manufacturing of the printer and the first breakdown). That is, it can be said that the higher the value of the MPBF, the higher the reliability. Here, in the above-mentioned breakdown, poor ejection such as dot omission is included, and one of the causes of the poor ejection is air bubbles in a liquid flow path. Then, in a case where the printing operation is continuously performed in the above printer, minute air bubbles gradually accumulate in the liquid flow path of the recording head. For this reason, a flushing process is required in which it is possible to further increase air bubble discharging ability, thereby more reliably preventing the poor ejection, and moreover, it is possible to more quickly stabilize the meniscus after the maintenance process.